docs: def handle_magic_line(line, cell, parser, namespace=None):
    """ Helper function for handling magic command lines given a parser with handlers set. """
    args = parser.parse(line, namespace)
    if args:
      try:
        return args.func(vars(args), cell)
      except Exception as e:
        sys.stderr.write(str(e))
        sys.stderr.write('\n')
        sys.stderr.flush()
    return None